CH. 14 Cardiovascular System: Blood Vessels, Blood Flow, and Blood Pressure Flashcards
1
Q
What two physical laws govern blood flow and blood pressure?
A
pressure gradients and resistance in the cardiovascular system
2
Q
How is the circulatory system a closed system?
A
there is no input or output but is rather just constant
3
Q
What is the equation for flow?
A
change in pressure/resistance
4
Q
What drives flow from high pressure to low pressure in the cardiovascular system?
A
pressure gradients (bulk flow)
5
Q
What is the change in pressure across the systemic circuit?
A
pressure in aorta (MVP) minus pressure in vena cava (CVP) just before it empties into right atrium
6
Q
What is change in pressure across the pulmonary circuit?
A
pressure in pulmonary arteries minus pressure in pulmonary veins
7
Q
T/F does blood in pulmonary circuit service the lungs
A
False; pulmonary circuit is meant only for gas exchange
8
Q
Is the pressure gradient greater in the systemic circuit or pulmonary circuit?
A
systemic circuit; resistance in pulmonary circuit is much less than resistance through the systemic circuit
9
Q
What three factors affect resistance to flow?
A
- radius of vessel
- length of vessel
- viscosity of fluid
10
Q
What is blood viscosity dependent on?
A
amount of RBCs and proteins - usually constant
11
Q
How does arteriole radius affect blood flow?
A
Vasoconstriction: decreased radius -> increased resistance
Vasodilation: increased radius -> decreased resistance
12
Q
What is total peripheral resistance?
A
combined resistance of all blood vessels within the systemic circuit
13
Q
What does vasoconstriction in network of blood vessels lead to?
A
increased resistance -> decreased flow
14
Q
What does vasodilation in network lead to?
A
decreased resistance -> increased flow
15
Q
How would you relate pressure gradients and resistance in the systemic circulation?
A
Flow = Cardiac output
Change in pressure = mean arterial pressure
Resistance = total peripheral resistance
16
Q
How do arteries act as a pressure reservoir?
A
they have thick, elastic arterial walls that push blood through system
- expand during systole and recoil during diastole
17
Q
What structural features make arteries a rapid transport pathway?
A
large diameter and little resistance
18
Q
What is compliance? What is meant by low compliance and high compliance?
A
measure of how the pressure of a vessel will change with a change in volume
- Low compliance: small increase in blood volume causes a large increase in pressure
- High compliance: large increase in blood volume is required to produce a large increase in pressure
19
Q
What is observed when measuring the blood pressure of a compressed artery?
A
turbulent flow produces Korotkoff sound
- pressure at first Korotkoff sound = systolic blood pressure
20
Q
What is observed when measuring the blood pressure of an uncompressed artery?
A
laminar flow, no sound
- pressure when sound disappears = diastolic blood pressure
21
Q
What is the equation for mean arterial pressure (MAP)?
A
MAP = [SP + (2 x DP)]/3
22
Q
What are resistant vessels?
A
arterioles; connect arteries to capillaries or metarterioles
23
Q
What factors affect arteriole radius?
A
- contraction state of smooth muscle in arteriole wall
- arteriolar tone: contraction level is independent of extrinsic influences
- vasoconstriction: increased contraction = decreased radius
- vasodilation: decreased contraction = increased radius
24
Q
What are the two functions of varying arteriole radius?
A
- controlling blood flow to individual capillary beds
2. regulating mean arterial pressure
25
What is regulation of blood flow to organs based on?
need
26
What local factors control vascular resistance?
1. changes in radius of arterioles
2. depends on contractile state of smooth muscle in walls of the vessel
3. local factors regulate, thereby regulate blood flow
27
What do changes associated with increased metabolic activity generally cause?
vasodilation
- carbon dioxide
- potassium
- hydrogen ions
28
What do changes associated with decreased metabolic activity generally cause?
vasoconstriction
| - oxygen
29
What is active hyperemia?
increased blood flow in response to increased metabolic activity
30
What occurs as a result of active hyperemia in organs?
1. increased metabolic rate
2. response to low oxygen and high carbon dioxide
3. increased blood flow
31
What is reactive hyperemia?
increased blood flow in response to a previous reduction in blood flow
32
What occurs when there is a blockage of blood flow to tissues?
metabolites increase and oxygen decreases but once blockage is released, metabolites are removed and oxygen is delivered as blood flow increases due to low resistance
33
What is a myogenic response?
change in vascular resistance in response to stretch of blood vessels in the absence of external factors
34
What is the purpose of myogenic auto-regulation of blood flow?
to keep blood flow constant
35
What are the big 4 local vasoactive substance and what are their effects on vascular smooth muscle?
1. oxygen: vasoconstriction
2. carbon dioxide: vasodilation
3. potassium ions: vasodilation (vasoconstriction at high concentrations)
4. acids (hydrogen ions): vasodilation
36
How is blood distributed during exercise?
- Dilation of vessels to skeletal muscle and heart increases blood flow to muscles
- Constriction of vessels to GI tract and kidneys decreases blood flow to these organs
37
What is mean arterial pressure dependent on?
total peripheral resistance
38
What is total peripheral resistance dependent on?
radius of arterioles
39
What extrinsic mechanisms regulate the radius of arterioles to control MAP?
1. sympathetic activity
| 2. hormones
40
How doe TPR and MAP increase when arteriolar radius is under sympathetic control?
norepinephrine binds to alpha adrenergic receptors and vasoconstriction is produced
41
What adrenergic receptors are present in arterioles to skeletal and cardiac muscle?
both alpha and beta 2 receptors
42
What binds to alpha adrenergic receptors and what occurs?
norepinephrine binds to alpha receptors and vasoconstriction occurs
43
What binds to both alpha and beta 2 receptors and what occurs?
epinephrine binds to both
- vasoconstriction at alpha receptors
- vasodilation at beta 2 receptors
44
What adrenergic receptor does epinephrine have a greater affinity for?
beta 2 receptors
45
What effect do sympathetic nerves have on arteriole radius?
vasoconstriction
46
What effect does epinephrine have on arteriole radius?
alpha adrenergic: vasoconstriction
| beta 2 adrenergic: vasodilation
47
What effect does vasopressin have on arteriole radius?
vasoconstriction
48
What effect does angiotensin II have on arteriole radius?
vasoconstriction
49
Which blood vessel has the slowest velocity of blood flow?
capillaries; slow blood flow enhances exchange between blood and tissue
50
What is allowed to move through continuous capillaries?
small water soluble molecules
51
What is allowed to move through fenestrated capillaries?
proteins, and in some cases blood cells
52
What are metarterioles and what do they function as?
they are intermediate between arterioles and capillaries that directly connect arterioles to venules
- function as shunts to bypass capillaries
53
What does contraction and relaxation of the smooth muscle of metarterioles do?
contraction: decrease blood flow through capillaries
relax: increase blood flow through capillaries
54
What are pre-capillary sphincters?
rings of smooth muscle that surround capillaries on the arteriole end
- only contract and relax in response to local factors
55
What does contraction and relaxation of pre-capillary sphincters do?
contraction: constricts capillary which decreases blood flow
relaxation: increases blood flow
56
What is the most common mechanism to exchange across capillary walls?
diffusion
- lipophilic: across membrane
- lipophobic: through channels
57
What are the 3 ways that exchange can occur across capillary walls?
1. diffusion
2. transcytosis: exchangeable proteins
3. mediated transport: in brain
58
What kind of movement is filtration across capillaries?
Movement out of capillary into interstitial space
59
What kind of movement is absorption across capillaries?
Movement into capillary from interstitial space
60
What are the 4 starling forces across the capillary walls?
1. Capillary hydrostatic pressure
2. Interstitial fluid hydrostatic pressure
3. Capillary osmotic pressure
4. Interstitial fluid osmotic pressure
61
What is the equation for net filtration pressure?
NFP = filtration pressure - absorption pressure
62
What is the role of the lymphatic system during blood circulation?
picks up excess filtrate and cleans and returns it to circulation
63
What are some factors that affect filtration and absorption across capillaries?
1. standing on feet - increases hydrostatic pressure
2. injuries
- when capillaries are damaged, they leak fluid and proteins
- histamine increases capillary permeability to proteins
3. liver disease
- decreases plasma proteins
- not enough plasma proteins lowers level of reabsorption
4. kidney disease
5. heart disease
64
What are venules?
connect capillaries to veins with little smooth muscle in walls
65
What allows unidirectional blood flow in veins and where are they present?
valves
- present in peripheral veins
- absent from central veins
66
What makes veins compliant vessels?
1. expand with little change in pressure
2. function as blood reservoir
3. 60% of the total blood volume in systemic veins are at rest
67
What 4 factors influence venous pressure and venous return?
1. skeletal muscle pump: one way valves in peripheral veins
- blood moves toward heart when contracted
- blood flows into veins between muscles when relaxed
2. respiratory pump:
- inspiration decreases pressure in thoracic and increases pressure in abdominal
- pressure in abdominal creates favorable gradient for movement to thoracic
3. blood volume
- increased blood volume -> increased venous pressure
- decreased blood volume -> decreased venous pressure
4. venomotor tone: smooth muscle tension in the veins
- increases central venous pressure
- decreases venous compliance
- increases venous return
68
What is the smooth muscle in the walls of veins innervated by?
sympathetic nervous system
69
What hormone acting at the alpha adrenergic receptors causes venous constriction?
norepinephrine
70
Where do lymphatic veins drain lymph fluid?
into the thoracic duct which empties into the right atrium
71
What are the three determinants of mean arterial pressure (MAP)?
1. heart rate
2. stroke volume
3. total peripheral resistance
72
What causes hypotension?
mean arterial pressure is less than normal and is caused by inadequate blood flow to tissues
73
What causes hypertension?
mean arterial pressure is greater than normal and is a stressor for heart and blood vessels when prolonged
74
How is mean arterial pressure regulated in the short term?
primarily neural control that regulates cardiac output and total peripheral resistance
- involves the heart and blood vessels
75
How is mean arterial pressure regulated in the long term?
primarily hormonal control that regulates blood volume and involves the kidneys
76
Lay out the negative feedback loop used in neural regulation of mean arterial pressure.
Detector = baroreceptors
Integration center = cardiovascular centers in the brainstem
Controllers = autonomic nervous system
Effectors = heart and blood vessels
77
What are baroreceptors?
pressure receptors that respond to stretching due to pressure changes in arteries
78
What are the two arterial baroreceptors?
aortic arch and carotid sinuses
79
What is the cardiovascular control center comprised of?
medulla oblongata which is the integration center for blood pressure regulation
80
What is the input (5) and output (2) of the cardiovascular control center?
Input:
- arterial baroreceptors
- low pressure baroreceptors
- chemoreceptors (oxygen and carbon dioxide)
- proprioceptors
- higher brain centers
Output:
- sympathetic nervous system
- parasympathetic nervous system
81
What occurs during autonomic output to cardiovascular effectors?
Parasympathetic input to SA node (decreases HR) -> AV node
Sympathetic input to SA node (increases HR) -> AV node -> ventricular myocardium (increases contractility) -> Arterioles (increases resistance) -> Veins (increases venomotor tone)
82
What is the framework of maintaining blood pressure at normal level?
baroreceptor reflex
- Detectors - baroreceptors
- Afferents - visceral afferents
- Integration center - cardiovascular control center
- Efferents - autonomic nervous system
- Effectors - heart, arterioles, and veins
83
What 3 hormones provide long term mean arterial pressure regulation?
1. epinephrine
2. vasopressin
3. angiotensin II
84
How does epinephrine increase mean arterial pressure?
1. acts on smooth muscle of arterioles (increases TPR)
2. acts on smooth muscle of veins (increases venomotor tone)
3. acts on heart (increases HR and SV)
85
How do vasopressin and angiotensin II regulate mean arterial pressure?
vasoconstrictors that increase TPR and MAP
86
What do low-pressure baroreceptors do and where are they found?
decrease in blood volume activates receptors which trigger responses that act in parallel with the baroreceptor reflex
- found in walls of large systemic veins and walls of atria
87
How does respiratory sinus arrhythmia regulate heart rate?
during inspiration:
- sympathetic activity increases -> heart rate increases
during expiration:
- parasympathetic activity increases -> heart rate decreases
88
What effect do chemoreceptors have on ventilation when carbon dioxide levels are increased in the blood?
carbon dioxide increases which in turn increases TPR and decreases HR
- MAP generally increases
89
How is thermoregulation mediated and how does it regulate cardiovascular responses?
through hypothalamus
- an increase in body temperature leads to: decrease sympathetic activity to skin
- vasodilation to skin
- increase heat loss to environment
90
What is more important to cardiovascular regulatory responses: baroreceptor reflex or thermoregulation?
thermoregulation
